When the snow falls and has been cleared to a thin layer, or it rains and starts to freeze, it is desirable to make a safe tractive surface to walk and drive on in parking lots, driveways and even walk ways. The prime method for making traction is to either melt the snow and/or ice, such as using salt, to expose a tractive surface below or spread a material tractive material, such as sand, to increase the traction on the slippery surface. The tractive action of the sand on the surface of the ice gives an immediate tractive surface. Further, a combination of salt and sand can be used where the salt acts to penetrate through the snow-ice barrier and eventually melt away the majority of the snow-ice and allow the tractive surface (i.e. the pavement or a gravel road) to be exposed while the sand provides the immediate increase in traction.
Several materials may be used as a consequence: salt, sand, sand/salt and salt with a liquid additive. Typically, for large application of these materials, a spreader is used to spread the material where it is desired to melt the snow or ice and/or to provide a tractive surface. Many spreaders will be a hopper spreader apparatus that has a hopper for storing the relevant material and then a spreading unit, such as a spinner, to spread the material on the desired surface.
In many instances, the material will use, at least in part, gravity to flow the material to a system for dispensing the material from the hopper to the spreading unit. The hopper will typically have angled sides that direct the flow of material toward the system that delivers the material to the spreading unit.
Unfortunately, the materials used to combat ice and/or snow as outlined above have very different angles of repose. The angle of repose or the critical angle of repose, of a granular material is the steepest angle of descent or dip relative to the horizontal plane to which a material can be piled without slumping. At this angle, the material on the slope face is on the verge of sliding. The angle of repose for dry salt is 36 degrees, damp sand is between 45 to 90 degrees and wetted salt is between 40 to 45 degrees.
The angle of repose for bagged salt for example is around 36 degrees, as a consequence the hopper sides on most spreading containers is 40 to 45 degrees. Thus, as the material is dispensed from the hopper, the salt will fall, due to the angle of repose, towards the dispensing system.
Moist sand, however, can have an angle of repose which is 90 degrees, meaning it can stand in a vertical column. The only way to make the column collapse is to disturb the base structure, in effect toppling the upper structure over. This can be done using a vibrator and/or remove the foundation base of the material to cause the mass of material to collapse on itself
One of the problems of the existing art is that there are two primary categories of spreaders, the drag chain spreader and the auger spreader. The drag chain spreader can flow a wide range of materials, however it is expensive in initial cost and upkeep. Repairs are extensive requiring prolonged down time for repairs. Very often an end user will buy a new unit in preference to repairs. Additionally, the spread quality of the drag chain spreader is not optimum and as a result too much material is consumed which is wasteful and expensive.
The auger spreader on the other hand flows high flow materials such as bagged salt, or very dry sand. Any amount of moisture added to the salt or sand causes the material flow characteristics to change drastically. This in turn requires the end user to change settings, such as on an inverted-v that is positioned above the auger to prevent jamming, on the auger spreader and in some cases may end up causing the auger to jam up. More particularly, the user is able to typically adjust the size of a flow path around the inverted-v towards the dispensing system to attempt to control the flow of material to the dispensing system. If this is not set correctly, the end user if not careful can end up with a hopper full of material that will not dispense. Further, for low flow shear resistant materials, e.g. wet sand, the material may stack up on top of the inverted-v.
Typically the flow resistant materials such as sand and wetted salt/sands are the lowest cost and yield excellent ice melting and pavement grip enhancing effects. Bagged salts on the other hand, which are high flow materials and easy to dispense, are more expensive and require special storage requirements.
The best way to destroy a cliff structure is to take out the foundational base of the material and then the top mass will cause the column to collapse on itself.
The best methods for removing this type of material from the hopper have previously involved a drag chain, which is essentially a large bottom section shearing off the bottom of the column and moving it out of the spreader unit in a slab shape. The slab is typically 15 inches wide by 3 inches tall. As the slab exits the drag chain it shears off into notable clumps as the material reaches its shear limit. The clumps drop onto the spinner and result in an uneven spread pattern on the outlet side of the spinner. Essentially the spreader pattern is not consistent but wavy or striped due to periodic clumps (also referred to as slumps) falling on the spinner. This is especially problematic for users who are concerned about even coverage and effective material distribution for either grip or melting efficacy.
A second method which is used with success requires high horsepower, expensive gearing, large auger flighting, robust auger shafting, vibrators, and in some cases inverted-v's, is the auger system. To cause the flow resistant material to move all these design elements must work in concert without jamming up the drive, without drawing a high load on the vehicle electrical system, and distributing the proper quantity of material down to the spinner.
The reason for the larger auger is to shear off the bottom of the material column. This large auger will see in excess of 1500 pounds of material weight. The auger is in turn is required to shear off the bottom and also move. The large auger must move at very slow speeds to allow the material to be dispensed at the proper rate. Matching the auger flighting so that the material is dispensed at proper rates can become a complex problem, requiring baffle adjustment, rpm adjustment, and vibrator impulses. Further, due to the large size and slow speed the large auger system can exhibit pulsing effects when moving the large slug of flow resistant material. The material will slump off in large chunks when exiting the large diameter auger much like the drag chain.
The problem with both systems is flowing high flow material, e.g. those that readily flow on their own and have an angle of repose of less than 40 degrees. The high flow material tends to flow past any flow gates and auger designs. Additionally, an inverted-v adjustment on an auger system for example that may be set for flow resistant materials is entirely different from a high flow setting.
Very often the auger will become overwhelmed in the high flow materials. The reason is that the setting for flow resistant material is designed to encourage the base of the material to collapse readily (i.e. has large openings to allow material to have minimum base support) as a result the high flow material will fall onto the auger and press with the equivalent weight of 20+ inches of material onto the auger which can cause the auger to jam.
The inverted-v, for example is designed to keep the full weight of material from exerting its weight on the auger. Flow Resistant material such as sand requires large openings to encourage the sand to gain access to the auger. Vibrators are used with flow resistant materials as well to encourage flow resistant materials to move through the larger openings. If the material is very flow resistant, the vibrator, however, may have an inverse effect, where the material instead of moving, becomes more flow resistant, or becomes packed together, eventually becoming a solid block of material and not being transferred out of the spreader at all. The material becomes bridged solidly in the spreader.
The spectrum of material flow index, or angle of repose, causes current spreader art or technology to adjust to the material type which involves variables in the spreader geometry. The auger system requires a user to be very aware of the material type and adjust the baffles of the spreader accordingly. As a result, auger spreader users typically use bagged salt, because the flow index is very predictable and consistent. Drag chain spreader users typically choose the drag chain spreader so as to be able to spread a wide range of materials. Unfortunately, they are stuck with poor spread quality, excessive flow quantity and road-transport-spillage especially when using high flow materials.
A further problem experienced by current spreaders is that the emptying profile for both drag chain spreaders and auger spreaders causes an uneven weight distribution during spreader use. More particularly, the spreader will typically dispense the material from the front of the hopper, i.e. furthest from the spinner, first. When the spreader is located in the bed of a vehicle, this translates into vehicle handling problems where the weight gradually shifts toward the rear of the vehicle which can cause the front steering to become less tractable.
As such, there is not a single system that currently handles materials that flow easily and that are flow resistant as well as provides a more uniform emptying profile.